PPS 15: Planning and Flood RiskAnnex A: Coastal and Tidal Flooding

A3 Coastal flooding may be described simply as the inundation of low lying coastal areas by the sea, or the overtopping or breaching of sea defences. It is an infrequent event in Northern Ireland but (as elsewhere) is typically characterised by flows that are more rapid than those associated with river flooding. Consequently, the risk to public safety can be higher during this type of event.

A4 Coastal flooding may be caused by seasonal high tides such as those driven by the spring neap tide cycle, storm surges and where increase in water level above the astronomical tide level is created by strong on shore winds or by storm driven wave action. Extreme conditions leading to coastal flooding are most commonly a result of a combination of two or more of these mechanisms. For example, the widespread flooding on the East Coast of England in 1953 was caused by a high spring tide, a deep atmospheric low and northerly gales combining to create a massive storm surge which breached coastal defences. In excess of 24,500 houses were inundated, 30,000 people had to be evacuated and over 300 people lost their lives.